The deposition of ultrasonic energy within the human body has numerous useful and promising medical applications. For example, ultrasound may be used for tissue ablation, diagnostic imaging, drug delivery, and other therapies which employ heat, cavitation, shock waves (e.g. destroying kidney stones) or other thermal and/or mechanical effects for therapeutic purposes.
A particularly advantageous use for ultrasonic energy deposition is thermal therapy (also known as hyperthermia, tissue ablation, and/or thermal surgery) which treats internal cancers and other internal diseases that respond to increases in body tissue temperature. Thermal therapy entails generating an ultrasonic energy beam and electrically focusing and controlling the energy beam to provide localized energy deposition in body tissue thereby heating the body tissue. Clearly, it is critical that the ultrasonic energy be focused to treat a desired target area of body tissue, and to avoid applying ultrasonic energy outside of the target area.
Prior art ultrasonic energy applicators typically have focusing and power difficulties. On the one hand, it is desirable to use high-frequency ultrasound to focus the beam more sharply and to improve power absorption in the target tissue thereby reducing near field and post-focus heating. On the other hand, higher frequencies generally result in large "grating lobes" (i.e. secondary focal points around the target area) that result in undesired heating, cavitation or other thermal/mechanical effects in non-targeted tissues.
The conventional technique for reducing grating lobes is to use small radiating elements having a center-to-center spacing of a half wavelength (or less) apart. However, small radiating elements have lower power capabilities, are less efficient, and are more costly to fabricate. Moreover, ultrasonic energy applicators that employ smaller elements are more difficult and expensive to produce since they require not only more radiating elements, but also additional power and control circuitry such as amplifier channels, phase shifters and wiring.
Therefore, it is an object of the present invention to provide an apparatus for ultrasonic energy deposition in body tissue with improved focusing capability.
It is another object of the present invention to provide an apparatus for ultrasonic energy deposition that reduces grating lobe magnitude.
It is still another object of the present invention to provide an apparatus for ultrasonic energy deposition that provides greater power, thereby reducing the time required to deposit a certain quantity of ultrasonic energy.
It is yet another object of the present invention to provide an apparatus for ultrasonic energy deposition that reduces the required number of radiating elements for a given grating lobe magnitude.
It is a further object of the present invention to provide a more efficient and cost-effective apparatus for ultrasonic energy deposition.
It is still a further object of the invention to provide an improved apparatus for ulrasonic energy deposition that can be used for tissue ablation, diagnostic imaging, drug delivery, and other therapies which employ heat, cavitation, shock waves or other thermal and/or mechanical effects for therapeutic purposes.